Articles made from thermoplastic resins are commonly utilized in the material-handling devices, electronic devices and business equipment, for example chip carriers, and printer and copier components in contact with moving paper such as paper paths--and moving components themselves--such as ink-jet printer penholders. Electrostatic dissipation is an especially important issue within the electronic industry because of the inherently insulating nature of organic polymeric materials. Electrostatic dissipation (or discharge) is defined as a transfer of electrostatic charge between bodies at different potentials caused by direct contact or induced by an electrostatic field. As electronic devices become smaller and faster, their sensitivity to electrostatic dissipation (ESD) increases.
The US Department of Defense Handbook 263 (DOD-HDK-263) defines three categories of plastics for use in ESD protection: antistatic, static dissipating, and conductive. Characteristics of each type are listed in Table 1. Conductive fillers such as carbon fibers can be incorporated into polymeric materials to modify the electrical properties to achieve any of these three characteristics. In particular, carbon fibers facilitate dissipation of static charge and provide enhanced electromagnetic shielding. (See, for example, U.S. Pat. Nos. 4,559,164 and 5,004,561).
TABLE 1 Categories of Materials for ESD/EMI Protection Material Category Material Description Antistatic Will not generate a charge. Will not allow a charge to remain localized on part surface. Refers to a material's ability to resist triboelectric charge generation. Static Will not generate a charge. Dissipating Will not allow a charge to remain localized on part surface. Can safely bleed an electric charge to ground. Surface resistivity between 10.sup.5 and 10.sup.9 Ohm/Sq. Conductive Will not generate a charge. Will not allow a charge to remain localized on part surface. Can ground a charge quickly. Will shield parts from electromagnetic fields. Surface resistivity &lt;10.sup.5 Ohm/Sq.